Experimental Study of Effect of Throat Height and Disturbances on Transonic Flow

摘要

The transonic flow consists of subsonic and supersonic state divided by sonic line.The sonic line is considered to be a kind of singular points, which is quite sensitive to a whole transonic flow field.Then, authors applied a piezo ceramic actuator to a transonic diffuser throat to control unsteady flow field under the above concept and clarified the effect of the throat height and frequencies of a piezo ceramic actuator on the transonic flow by mean of high speed schleiren visualizing technique and unsteady wall static pressure measurements.In this report,the effect of the throat height and frequencies of piezo ceramic actuator are studied in order to apply more practical conditions in which separations of a boundary layer in a diffuser take place.That is, the positons of a starting shock wave are affected by pressure recovery downstream of the starting shock wave.Authors have figured out the parameters which cause the less pressure recovery resulting in unsteady shock wave behavior.It is found that the starting shock wave stands at two averaged positions even under the constant pressure ratio, which is referred to as a bistable shock behavior.The shock wave in case of the throat height of 1 mm and pressure ratio of 1.5 is stabole for all frequencies.Therefore the disturbances from the diffuser throat for the throat height 1mm is expected to affect directly to the starting shock wave without any inflnence from downstream of the shock.FFT analyses of shock wave behavior for three throat heights and the frequency of 100Hz.suggests that the shock behavior for the throat height of lmm has the quite clear dominant frequency compared to the other two throat heights.Accordingly, the 1mm throat height diffuser under the pressure ratio of 1.5 is found to be promising condition to control transonic flow.